A New Variant B Chromosome in Auchenipteridae: The Role of (GATA)_n and (TTAGGG)_n Sequences in Understanding the Evolution of Supernumeraries in <b><i>Trachelyopterus</i></b>

Abstract

Basic and molecular cytogenetic techniques were carried out in 3 Neotropical region populations of catfishes, two of Trachelyopterus galeatus (one from the marshlands of Paraguay River basin and another from Lago Catalão, Amazon River basin) and one of Trachelyopterus porosus, a sympatric population to T. galeatus from the Amazon River basin. This study aimed to describe and understand the structure and evolution of Trachelyopterus B chromosomes, mainly through physical mapping of repetitive elements. A diploid number of 58 chromosomes was found for all individuals, as well as the presence of B chromosomes. For T. porosus this is the first report of a supernumerary. The sympatric species of T. galeatus and T. porosus from Amazon River had 1–3 B chromosomes and T. galeatus from Paraguay River had 1–2 B chromosomes, all of them showed intra- and interindividual numerical variation. Two females of T. porosus exhibited a new variant B chromosome (B2), previously not seen in Auchenipteridae, which might have originated from B1 chromosomes. All B chromosomes were entirely heterochromatic. In contrast to all complement A and B2 chromosomes, in which the telomeric sequences were found in the telomeric regions, B1 chromosomes of all populations were totally marked by (TTAGGG)n probes. (GATA)n sequence sites were found through all complement A chromosomes, but B1 and B2 chromosomes exhibited only a clustered block in one of the chromosome arms. The most frequent B chromosomes (B1) in all populations/species, including those previously studied in Auchenipteridae catfishes, share the following characteristics: totally heterochromatic, small, metacentric, with accumulation of repetitive (TTAGGG)n sequences, and a low number of (GATA)n copies, which might suggest a common ancient origin in Trachelyopterus species/populations.

Karyotype Evolution of Talking Thorny Catfishes Anadoras (Doradidae, Astrodoradinae): A Process Mediated by Structural Rearrangements and Intense Reorganization of Repetitive DNAs

“…According to Takagui et al [2021], the ancestral diploid number for the Doradidae family still remains as an open question, but several lines of evidence support the 2n = 58 chromosomes as a plesiomorphic feature in the family and as the likely ancestral karyotype configuration. Furthermore, this diploid number also occurs in most species of Auchenipteridae [Lui et al, 2009[Lui et al, , 2010[Lui et al, , 2013a[Lui et al, , 2013b[Lui et al, , 2015[Lui et al, , 2021Felicetti et al, 2021;Machado et al, 2021;Santos et al, 2021], the sister group to Doradidae family [Arce et al, 2013;Birindelli, 2014;Sabaj and Arce, 2021].…”

Are scattered microsatellites weak chromosomal markers? Guided mapping reveals new insights into Trachelyopterus (Siluriformes: Auchenipteridae) diversity

“…In chromosomal mapping, although studies are still scarce for most species, they have provided a useful tool for understand the genome and chromosomal evolution of many different taxa [ 18 – 20 ]. They can be cytogenetically identified in large accumulations on a few chromosomal pairs [ 20 , 21 ] or with scattered signals throughout the chromosomes [ 20 , 22 , 23 ]. Furthermore, SSRs are commonly described associated to heterochromatic regions (e.g., [ 24 , 25 ]), often participating in its origin and increase (cHC) (for reviews, see [ 26 – 28 ]), and with crucial roles in the origin and evolution of specific chromosomes, mainly B chromosomes [ 22 , 23 , 29 ] and sex chromosomes [ 21 , 30 , 31 ].…”

“…They can be cytogenetically identified in large accumulations on a few chromosomal pairs [ 20 , 21 ] or with scattered signals throughout the chromosomes [ 20 , 22 , 23 ]. Furthermore, SSRs are commonly described associated to heterochromatic regions (e.g., [ 24 , 25 ]), often participating in its origin and increase (cHC) (for reviews, see [ 26 – 28 ]), and with crucial roles in the origin and evolution of specific chromosomes, mainly B chromosomes [ 22 , 23 , 29 ] and sex chromosomes [ 21 , 30 , 31 ]. However, in complement A chromosomes and populations without sex or B chromosomes, the cytogenetic studies are still concentrated only in the type of array and presence or absence of the marker, considering the whole karyotype [ 32 , 33 ].…”

“…[ 23 , 90 ]; whereas the SSR (GATA) n sites were described in only three species: T . galeatus [ 22 , 23 ], T . porosus [ 22 ] and Trachelyopterus aff.…”

“…galeatus [ 22 , 23 ], T . porosus [ 22 ] and Trachelyopterus aff. coriaceus (cited as Trachelyopterus sp.)…”